The primary objective of the proposed investigation is the development of an effective, safe, and clinically applicable method for the assessment of regional myocardial nutrient blood flow and for the localization and sizing of myocardial infarcts. The approach to be employed utilizes positron emitting monovalent cations which act as K ion analogs and are actively transported into myocardial cells from the coronary circulation with high efficiency. Imaging will be accomplished by a high resolution multi-crystal positron camera using multiple coincidence detection of positron annihilation radiation collimation. A data rate capacity of 5 x 10 to the 4th power coincident events per second allows sequential images of fractional second duration to be obtained, with spatial resolution less than 1 cm. Tracers to be studied include 13NH4 plus and 38 K ion 38, short half-lived tracers (T 1/2 equals 10 min and 7.7 min respectively) produced in Massachusetts General Hospital cyclotron. Scintigraphic images obtained with the positron camera show homogeneous uptake in the normally perfused ventricle following intravenous or intracoronary infusion of 13NH4 plus, and well delineated areas of decreased uptake after ligation of distal branches of the left coronary system. Systematic studies are proposed to allow: (1) radiopharmaceutical development; (2) delineation of monovalent cation transport in normal, ischemic and reperfused myocardium; (3) development of optimum techniques for in vivo myocardial scanning using the positron camera, including novel new approaches to imaging of 3-dimensional distribution of positron-emitting radionuclides in myocardium; (4) completion of development of instrumentation and facilities suitable for myocardial scanning in patients with acute and chronic ischemic heart disease, and determination of the role of myocardial scanning in the evaluation and care of these patients.